Do you have a Conbee/ConbeeII Zigbee dongle or a Digi Xstick? We have found decent success with the Conbee dongles, to support Tradfri buttons, including the one you linked to.
If not new out of the box, or had already been paired, go through the factory reset process on the remote, then click the “+” on Things page scan, then wait. It takes a while sometimes for the Zigbee scanning/pairing/provisioning process to complete before it shows up on the page.
Also, there are ways to debug the Zigbee adapter. Hopefully this wiki page is up to date: